There is NO SUCH THING as "too much caffeine"
If I have an average amount of caffeine (a soda, a cup of coffee) it puts me to sleep. Any more than that and I get jittery. 5 Hour Energy's work great for me, though.
When I get used to something it relaxes me and makes me sleepy. It's weird because that applies to almost everything. Metallica and Dragonforce songs both make me drowsy, and if I've played a game too much it will make me nod off in the middle of playing it.